1. Field of the Invention
The present invention relates to the field of internal combustion engines.
2. Prior Art
One of the problems encountered in diesel fuel injection is the satisfactory achievement of fuel injection throughout its operational range, and particularly at its two operational extremes, namely, a sufficiently small injection rate with good atomization at idle and low engine loads, and a sufficient injection rate at speed and under full engine load. Also it is recognized that better engine performance may be achieved if the normal injection is preceded by a small pilot injection, that is, an injection of a relatively small amount of fuel, preferably with a short delay before the normal injection, to allow combustion to begin by the time the normal injection begins. Consequently, good control of the injectors and the injection rates is required.
In an intensifier type injector, an actuation fluid, which may be, by way of example, fuel or engine oil, controllably pressurizes a relatively large piston, which in turn pushes on a relatively small piston to pressurize fuel for injection. Thus the fuel pressure for injection will be intensified relative to the pressure of the actuation fluid by the ratio of the two piston areas, which ratio may be, by way of example, in the range of 2 to 10. In such injectors, the injection flow rate could be controlled by varying the pressure in the rail supplying the actuation fluid pressure, though doing so is normally a relatively slow process. In particular, because of the compressibility of the actuation fluid, substantial reduction in rail pressure faster than it would normally decay without replenishment would require dumping significant amounts of actuation fluid to a low pressure vent, dissipating significant energy in the process. Similarly, increasing rail pressure requires forcing significant amounts of actuation fluid into the rail sufficiently faster than the actuation fluid is being used to make up for the compression of the actuation fluid in the rail as the pressure increases. Thus, varying rail pressure is something that can be considered over a number of engine revolutions, but not for injection cycle to injection cycle, and particularly not for pilot injection versus main injection.